1. Field of the Invention
The subject matter disclosed herein relates to a piston for use in a reciprocating internal combustion engine. The piston has a slidably mounted crown forming part of a gas chamber at the top of the piston. The gas chamber acts as a gas spring to suspend the piston crown.
2. Related Art
Designers of reciprocating internal combustion engines, in general and, more specifically, diesel engines, are faced with increasingly stringent regulatory requirements relating to exhaust emissions. More specifically, future regulations will require less emission of oxides of nitrogen (NOx), particulate matter (PM), and unburned hydrocarbons (HC). It is known that an effective way to control NOx is to decrease the peak temperatures within the combustion chamber, as well as by decreasing the available oxygen through exhaust gas recirculation (EGR). Both of these remedial actions tend, however, to cause increases PM and HC emissions. Fixation of nitrogen occurs at a very high rate above 2000° K. On the other hand, hydrocarbon formation tends to increase sharply below 1500° K. Accordingly, if peak combustion chamber temperature is lowered, NOx may be reduced, but at the expense of producing more hydrocarbon. Late ignition timing, sometimes termed ignition timing retard, may be used to reduce NOx formation. This will have the effect of causing cylinder temperature to fall below 1500° K, resulting in higher hydrocarbon, and increased fuel consumption.
It would be possible to simultaneously produce beneficial results regarding emissions of NOx, PM, and HC while not adversely affecting brake specific fuel consumption if peak temperatures could be limited but, nevertheless, be held above 1500° K long enough to completely consume all the fuel.
It is desirable to have a pressure reactive piston allowing engine operation in a regime which simultaneously reduces the formation of NOx, PM, and HC, while not adversely affecting fuel consumption.